Symptoms
A new domain was added to existing subscription, and when created new users all of them are held by tasks at task manager, and all users were stuck in transitional states - updating or deleting.
Cause
The cause of the many un-processed tasks is that one has failed and was blocking all others from execution. See KB#2247 for additional details regarding the cause.
Resolution
The task may fail with timeout, please check the article regarding tasks failing with timeout, KB#116374, try to re-run it and troubleshoot in accordance with Windows Provisioning troubleshooting.